Super slow RAID speeds - Dell PERC

[WackyWRZ]

Hey all,

I'm in the process of replacing my old home server with a new one and am running into some RAID performance issues. This is all on a Dell R710 server with a Perc 6/i hardware RAID card. I am running ESXi 6.0 and the guest OS is Windows 2012R2. The setup that I am having issues with are 2x Seagate Barracuda Green 2TB SATA drives.

I am trying to set these up in a RAID1 and the read/write performance is horrible. I can tell copying files its taking forever. Using CrystalDiskMark OR HDTune these are the sequential numbers I am seeing. Random R/W is even worse!

Single Drive READ- 120-150MB/s
Single Drive WRITE- 115-130MB/s

RAID1 Read: 50-70MB/s
RAID1 Write: 35-40MB/s

I started thinking maybe its because these are 5900 "green drives". I whipped out a pair of 7200 750GB SATA drives and got the same sort of results. Good performance on single drives but terrible on RAID1. The BBU is fine, the Read-Ahead and Write-Back caches are enabled. The array is also fully initialized, so that is not taking up any of the disk I/O. I also have a 3x 300GB SAS array on this controller for the OS and general storage - and its showing read/write performance in the 300MB/s range.

I am not sure what the issue could be, but I would think RAID1 would have equal or slightly less performance than a single drive. All BIOS and Firmware is completely up to date. I am thinking that I might just present the drives to the OS bare and either use Storage Spaces or something like DrivePool/Drive Bender to get my mirror... I don't have a whole lot of experience with RAID arrays outside of RAID5/6. I also don't have much experience with the Dell PERC so I would appreciate any suggestions that are offered!

 

[xyvyx]

I wonder if this could be an alignment issue... I thought the PERC software actually handled this (mirrored volumes behave fine on my R730xd I just configured).
Try running this from a command prompt:
wmic partition get BlockSize, StartingOffset, Name, Index

 

[Cerb]

What are the write cache settings?

 

[alyarb]

I know you don't want to hear it but PERC6 is really junk in my experience. We try to only use H700 or H710p if we require compatibility with OpenManage.

You really cannot draw ANY useful comparisons to a 730xd. You probably have a H730p controller in that box, which is an entirely different league than a 6+ year old controller like the 6i.

If you can afford a R730xd, but can't afford to swap out that 6i for a H710, then just update the firmware and disable cache on the green RAID1.

If that doesn't work, put the green drives in RAID0 and repeat your testing just so you have another data point. If your results are similar, then you have to separate the two green drives and I don't believe there is a JBOD mode. So you'll have to put each green drive into a single-drive RAID0 array. Then do your testing again. Inch it closer and closer to native performance, and then present the bare drives to 2012 R2 and do a software mirror in storage spaces.

 

[386DX]

Do you have a BBU with your RAID card? With out a BBU (battery backup unit) almost every hardware RAID card will turn off caching to not risk Data Integrity. With a single drive it doesn't matter but with any RAID it will be slow as essentially all drives must fully read or write the data before continuing.